The present invention relates to distance measurements and, more particularly, to a method for estimating the accuracy of an optical probe used to measure the shape of a workpiece.
Optical probes are used in manufacturing to measure the shape of a workpiece, by scanning the surface of the workpiece using such a probe and measuring a series of distances to the surface of the workpiece. Representative optical probes that are used for this purpose include the WIZ probe, manufactured by Nextec of Tirat Hacarmel, Israel, the OTP6M optical trigger probe system, manufactured by Renishaw PLC of Wotton-under-Edge, UK, and the ITS Laser Triangulation Sensor Heads, manufactured by Gesellschaft fur Messtechnik mbH of Aachen, Germany. The accuracy of these probes is measured by calibrating them, using standard objects of known shape. In practice, this is not totally satisfactory, because the accuracy of the measured distances to real workpieces depends, in general, on surface properties of the workpieces, particularly surface finish, but also surface color, surface emissivity and other optical characteristics; and the surface properties of such workpieces generally are different than the surface properties of the standard calibration objects.
There is thus a widely recognized need for, and it would be highly advantageous to have, a method of estimating the accuracy of measurements of distance from an optical probe to a workpiece, based on those measurements themselves, and not on measurements made using a standard calibration object.